The present invention relates to an optical disk apparatus, and more particularly to an optical disk apparatus for carrying out a defocus regulation in a state in which a servo control of focusing and tracking is performed.
In an apparatus for reproducing data recorded on an optical disk, the following technique has been proposed in order to enhance precision in a tracking servo and to improve the signal quality of a reproducing signal (which will be referred to as a first related art). More specifically, in the technique, focus-ON is carried out by executing a servo control of focusing and track-ON is carried out by executing a servo control of tracking as shown in FIG. 4 (a servo control of a CLV can also be carried out together in the technique). In this state, there is carried out a defocus regulation for adding an offset voltage to a focus error signal (which will be hereinafter referred to as an FE signal) in such a manner that a jitter amount of an RF signal is a minimum (an amplitude of the RF signal is a maximum).
Then, a tracking servo is turned OFF and a balance of a tracking error signal (which will be hereinafter referred to as a TE signal) (which will be hereinafter referred to as a TE balance) is regulated (a regulation for setting an offset of the TE signal to be zero) in such a manner that a peak voltage and a bottom voltage of the TE signal are symmetrical with a reference voltage when a beam spot crosses a track. More specifically, the TE balance is regulated in a state of a just focus in which a focal position of the beam spot is placed on a recording plane with high precision. For this reason, there is not generated a shift of the TE balance which is caused when the defocus regulation is carried out after the regulation of the TE balance. Therefore, a stable tracking servo is carried out (for example, see JP-A-2000-76668).
Moreover, the following technique has been proposed (which will be referred to as a second related art). More specifically, in the technique, a servo control of focusing is carried out to turn ON focusing in a reproduction of a CD, and subsequently, a defocus regulation for adding an offset voltage to a focus error signal (which will be hereinafter referred to as an FE signal) in such a manner that an amplitude of an RF signal is maximized. Then, a TE balance is regulated in such a manner that a peak voltage and a bottom voltage of a TE signal are symmetrical with a reference voltage when a beam spot crosses a track. Thereafter, a servo control of tracking is carried out. Accordingly, the servo control of the tracking is carried out in a state of the best TE balance. Consequently, a stable tracking servo is carried out (for example, see JP-A-8-339550).
In the case in which the first related art is used, however, the following problems arise. More specifically, in some cases in which an optical disk which is a reproducing target is a CD-R or a CD-RW in an apparatus for generating a TE signal by a DPD method, there is brought a state of detrack in which a beam spot is not positioned on a center of a track due to a shift of an attachment position of a PDIC that is a unit for detecting a reflected light or a variation in a sensitivity of a region of the PDIC divided into four parts also when the regulation of the TE balance is carried out.
When the defocus regulation is carried out in this state, the TE balance is lost due to the state of the detrack. In some cases in which the TE balance is lost, precision in the detection of the offset voltage to be added to the FE signal is deteriorated to cause a situation in which an offset voltage separated from an optimum value is added to the FE signal (a situation in which the defocus regulation cannot be carried out well).
Referring to the second related art, the defocus regulation is carried out in a state of track-OFF in which the servo control of the tracking is not performed. More specifically, in a state in which a signal indicative of data cannot be reproduced continuously, an offset voltage for giving a maximum amplitude of the RF signal is detected. For this reason, the precision in the detection of the offset voltage for giving the maximum amplitude of the RF signal is apt to be deteriorated. Therefore, there is a problem in that precision in the defocus regulation is deteriorated easily.